Conventionally, a transmission system which can transmit a signal inexpensively at high speed in a severe noise environment such as in a railroad car is needed.
As the transmission system of this type, there is known a transmission system for railroad, which builds a general-purpose local area network (LAN) over a plurality of railroad cars, and transmits video data and control data between the railroad cars (see Patent Literature 1, for example).
The transmission system for railroad described in Patent Literature 1 is described below referring to FIG. 7. FIG. 7 is a configuration diagram illustrating the conventional transmission system for railroad.
In FIG. 7, a LAN hub 51 is provided on each of a plurality of railroad cars 50 coupled with each other. Moreover, a vehicle information central device 52 and an operator seat screen device 53 are provided on each of both of lead cars 50.
The LAN hubs 51, the vehicle information central devices 52, and the operator seat screen devices 53 are connected with one another via a LAN main line 54. Moreover, the LAN main line 54 is connected by crossovers 55 between the railroad cars 50. A signal can be transmitted inexpensively at high speed by applying the general-purpose LAN to the transmission system for railroad.
However, when a signal is transmitted between the railroad cars 50, the signal is transmitted via the crossover 55, and hence there is a problem that transmission characteristics are degraded by a transmission loss of the transmission line, characteristics of the crossover 55, noise superimposed on the crossover 55, and the like.
Now, a general method for restraining a degradation of the transmission characteristics in a transmission system is described referring to FIG. 8. FIG. 8 is a configuration diagram illustrating a general transmission system which can restrain the degradation of the transmission characteristics.
In FIG. 8, the transmission system includes a transmitter 61, and a receiver 63 connected to the transmitter 61 via a transmission line 62.
The transmitter 61 includes a transmission amplifier 64 for stepping up a signal amplitude of an input signal with a gain G. The receiver 63 includes an attenuation circuit 65 for attenuating a signal amplitude of an input signal by G times.
In other words, a signal voltage Vo of the transmission signal is stepped up to GVo by the transmission amplifier 64, and is output to the transmission line 62 as an output signal having the signal amplitude GVo. Moreover, the output signal transmitted over the transmission line 62 is input to the receiver 63 as an input signal having a signal amplitude Vin. The signal amplitude Vin of the input signal is attenuated by the attenuation circuit 65 by G times into a received signal having a signal amplitude Vrcv.
According to this transmission system, the signal amplitude Vo of the transmission signal is stepped up by G times, and the SN ratio for noise superimposed on the transmission line 62 is thus improved by G times at most. Therefore, the degradation of the transmission characteristics can be restrained.